The present invention relates to a high-frequency power amplifier (high-frequency circuit module), a wireless communication apparatus which incorporates the high-frequency circuit module, and a wireless communication system, and particularly to a wireless communication technique for controlling the output power of a high-frequency power amplifier accurately thereby to perform the communication with a stable output power.
Wireless communication apparatus for mobile telephone and portable telephone incorporate in their transmission output stage a power amplifier formed of MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) and GaAs-MES (Metal Semiconductor) FETs in cascade connection.
Portable telephone (portable terminal) systems have been generally designed such that each portable unit varies the output power to match with the communication environment in response to the power control signal sent from the base station thereby to prevent crosstalk with other units.
Trends of high-frequency power amplifiers are described in publication xe2x80x9cNikkei Electronicsxe2x80x9d, pp. 115-126, published by Nikkei BP Corp. on Jan. 27, 1997. The article of this publication covers the standard scheme of the 900 MHz cellular portable telephone in North America and the GSM (Global System for Mobile Communications) in Europe.
Another publication xe2x80x9cHitachi Reviewxe2x80x9d, Vol.79, No.11 (1997), pp.63-68, published by Hitachi Review Corp. includes an article on the high-frequency analog signal processor IC for the digital cellular GSM/EGSM. This publication discloses by block diagram a control scheme of a power amplifier module based on a detected power signal provided by a directional coupler.
In a digital portable telephone system (cellular telephone system) as shown in FIG. 17, a base station 1 sends a power control signal from its antenna 2 to each mobile terminal unit (portable telephone unit) 3 having an antenna 4 so that the unit operates at a minimal transmission power necessary for communication, thereby to prevent crosstalk with other units. The power control signal is either a high-level power signal 5 or a low-level power signal 6.
The mobile terminal unit includes an automatic power control (APC) circuit, which operates in response to the received power control signal to adjust the output power by varying a power control signal Vapc to be fed to the control terminal of the high-frequency power amplifier of the transmission output stage.
The portable telephone unit is required to have a high output gain and efficiency and, at the same time, a low power consumption at the time of small-power operation. It is difficult to meet these requirements in the entire output power range, and therefore the high-frequency power amplifier is currently designed to switch in its response characteristics between low-power mode and high-power mode across a border power level of about 29 dBm, thereby accomplishing lower power consumption during small-power operation and higher operational efficiency.
FIG. 18 and FIG. 19 show the circuit arrangement of a 3-stage high-frequency power amplifier including three transistors (MOSFETs: Metal Oxide Semiconductor Field Effect Transistors) in cascade connection. The first-stage transistor (1stTr), second-stage transistor (2ndTr) and third-stage transistor (3rdTr) are all n-channel NMOS transistors.
The power amplifier receives a high-frequency input signal RFin on its input terminal 10, which is connected to the gate electrode of the transistor 1stTr via a coupling capacitor C10. The 1stTr has its drain electrode as output terminal connected via a coupling capacitor C11 to the gate electrode of the 2ndTr, with the drain electrode as output terminal thereof being connected via a coupling capacitor C12 to the gate electrode of the 3rdTr (last-stage transistor), with the drain electrode thereof being connected to an output terminal 11, which releases a high-frequency output signal RFout.
The power amplifier receives on its control terminal 12 a power control signal Vapc, which is delivered to the gate electrodes as control electrodes of the transistors (1stTr,2ndTr and 3rdTr). The 1stTr has its gate electrode biased by the voltage of power control signal Vapc with the rendition of voltage division by resistors R1 and R2, and the 2ndTr has its gate electrode biased by the voltage of Vapc with the rendition of voltage division by resistors R3 and R4.
The 3rdTr has its gate electrode biased by the voltage of Vapc with the rendition of voltage division by resistors R5 and R6 having resistance values of 10 k* and 30 k*, respectively, for example, and the further rendition of control by two transistors Q11 and Q12. The transistor Q11 has its drain electrode connected to the resistor R6 and its source electrode grounded, and operates for switching. The transistor Q12 has its gate electrode connected to the drain electrode of the Q11, its drain electrode connected to the gate electrode of the 3rdTr, and its source electrode grounded (connected to GND).
The transistors (1stTr,2ndTr and 3rdTr) have their drain electrodes connected to a first reference voltage terminal (power voltage terminal) 13 and supplied with a power voltage Vdd.
When the terminal unit 3 receives a high-level power signal from the base station 1, the signal turns on the transistor Q11, causing the transistor Q12 to have its gate electrode pulled to GND. Consequently, the 3rdTr operates to have a linear high-mode response as shown in FIG. 2.
In contrast, a low-level power signal from the base station 1 does not turn on the transistor Q11 and the transistor Q12 operates by having on its gate electrode the voltage of the voltage division node of the resistors R5 and R6. Consequently, the 3rdTr operates based on the nonlinear (saturated) low-mode response as shown in FIG. 2.
On the characteristic graph of FIG. 2, input voltage region A is of low-power mode selected by the low-level power signal, and input voltage region B is of high-power mode selected by the high-level power signal.
The inventors of the present invention have devised a bias circuit for making a transition of the 3rdTr gate voltage from the low-power mode to the high-power mode at a high-frequency power level of about 29 dBm, i.e., at a power control signal Vapc of about 1.25 V, and the present invention owes to this technique.
Accordingly, an object of this invention is to provide a high-frequency power amplifier and a wireless communication apparatus which are capable of selecting a high-power mode or low-power mode automatically without using the power control signal sent from the base station.
Another object of this invention is to provide a high-frequency power amplifier which is capable of controlling the output power characteristics accurately.
Still another object of this invention is to provide a wireless communication apparatus which is capable of controlling the output power characteristics accurately, thereby to perform stable communication.
These and other objects and novel features of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings.
Among the affairs of the present invention disclosed in this specification, representatives are briefed as follows.
(1) The inventive wireless communication apparatus comprises a high-frequency power amplifier for transmission, a detection means which measures the output power of the power amplifier, and a power control circuit (automatic power control circuit) which controls the output power of the power amplifier based on information provided by the detection means. The high-frequency power amplifier includes an amplifying system which has multiple amplifying stages and is connected between the input and output terminals, and bias circuits which supply bias voltages to transistors of the respective amplifying stages. The bias circuits, which supply bias voltages to the multiple amplifying stages excluding a first amplifying stage (last amplifying stage), are each made up of multiple resistors. Each of these bias circuits divides with the resistors the voltage of an entered power control signal to produce a bias voltage, which has a linear response to the control signal for low-power mode, to be fed to the control terminal of the amplifying stage. The bias circuit which supplies a bias voltage to the first amplifying stage (last amplifying stage) includes a circuit which produces a bias voltage which has a nonlinear response to the control signal for high-power mode.
The bias circuit for the last amplifying stage is made up of a voltage division circuit which divides the voltage of the power control signal and delivers the divided voltage to the control terminal of the last amplifying stage, and a control transistor having its control electrode connected to the voltage division node of the voltage division circuit, its first electrode connected to the resistor on the lower voltage side relative to the voltage division node among the resistors of the voltage division circuit, and its second electrode grounded.
In the inventive wireless communication system which avails for wireless communication among wireless communication units by way of a base station, the base station does not have a function of sending a power control signal, and each wireless communication unit has a means of controlling its power mode without using a remote power control signal. The power mode control means includes a bias circuit which supplies a bias voltage to the last amplifying stage of the high-frequency power amplifier.
The inventive wireless communication unit comprises:
a high-frequency power amplifier for transmission;
detection means for measuring the output power of the power amplifier; and
an automatic power control circuit which controls the output power of the power amplifier based on information provided by the detection means,
the power amplifier including:
an input terminal;
an output terminal;
a control terminal which receives a power control signal;
an amplifying system which has multiple amplifying stages and is connected between the input terminal and the output terminal; and
a bias circuit which is connected to the control terminal and adapted to supply a bias voltage, which has a nonlinear response to the power control signal received on the control terminal, to the last amplifying stage,
the bias circuit constituting the power mode control means.
(2) The bias circuit for the last amplifying stage in the above-mentioned item (1) comprises:
a voltage division circuit which divides with multiple resistors the voltage of a power control signal and delivers the divided voltage to the control terminal of the last amplifying stage;
a control transistor having its control electrode connected to the voltage division node of the voltage division circuit, its first electrode connected to the resistor on the lower voltage side relative to the voltage division node among the resistors of the voltage division circuit, and its second electrode grounded; and
a current sensing transistor having its control electrode connected to the control electrode of the transistor of the last amplifying stage and releasing a voltage indicative of the sensed current from its first electrode.
According to the above-mentioned arrangement of item (1),
(a) The high-frequency power amplifier has its bias circuit for the transistor 3rdTr of the last amplifying stage adapted to switch the gate voltage characteristics from nonlinear response to linear response at a power control signal Vapc of about 1.2 V. This switching operation is equivalent to the switching from low-power mode to high-power mode in response to the power control signal sent from the base station.
(b) In consequence of item (a), the wireless communication unit does not need to have a processor for dealing with the power control signal from the base station and thus can reduce the number of component parts.
(c) In contrast to the conventional high-frequency power amplifier, in which the power mode switching circuit is formed by being monolithic on the semiconductor chip of the power amplifier, the inventive high-frequency power amplifier, which is rid of the reception of a power control signal (power mode control signal), does not need to include a switching transistor and associated input terminal (pad) on the semiconductor chip and thus can reduce the chip area.
(d) In consequence of item (c), the semiconductor chip for the high-frequency power amplifier can be made much smaller.
(e) In consequence of item (d), the number of semiconductor chips formed on a semiconductor wafer can be increased, the production yield can be improved, and the cost of semiconductor chips can be lowered.
(f) For a wireless communication system in which all portable telephone units are rid of remote power mode switching, the base station does not need to transmit a power control signal and can simplify the facility.